This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The identification and characterization of the trans-synaptic adhesion proteome may prove sufficient to break the synapse code. Determination of the trans-synaptic adhesion proteome may prove central to our eventual understanding of neuronal synaptic circuitry and brain wiring and in turn organism behavior. Historically, Neurexins (NRXNs) have been considered the most-likely presynaptic protein responsible for post-synaptic differentiation. NRXN protein expression is highly regulated (3 genes, alternative promoters, and massive alternative splicing) and it has been proposed that NRXNs may be present in thousands of isoforms within the mammalian brain.